The invention relates to thermal barrier coating compositions, processes for applying same and articles coated with same. More particularly, the invention relates to thermal barrier coating compositions designed to withstand sand infiltration, processes for applying same and articles coated with same.
The degradation of turbomachinery parts due to sand related distress of thermal barrier coatings (“TBCs”) is a concern with respect to all turbomachinery in use in the Middle East. Sand related distress is responsible for the premature spallation of TBCs and oxidation of turbomachinery and their parts. The mechanism of such sand related distress is the penetration of the TBCs by molten sand. During its useful life, sand may enter the turbomachinery, agglomerate and become molten upon the TBC surface. Typically the surface temperature of the turbomachinery is higher than the melting point temperature of the sand. As a result, the agglomerated sand particles become somewhat molten, penetrate the TBC and reach the ceramic/metallic interface. The failure of the TBC occurs by a combination of molten sand attacking the thermally grown oxide at the ceramic/metallic interface as well as the reduction in strain tolerance, of the fully infiltrated TBC, to thermal cycling. Failure of the TBC occurs by spallation which exposes the part's surface to the elements, thus causing the accelerated oxidation of the turbomachinery part in conjunction with molten sand attack.
Consequently, there exists a need for a thermal barrier coating designed to resist sand related distress.